Process for lapping hypoid gearsets

ABSTRACT

GEAR TEETH OF AUTOMOTIVE HYPOID GEAR SETS ARE LAPPED WITH AN AQUEOUS BASE LAPPING COMPOSITION. THE LAPPING COMPOSITION IS APPLIED CONTINUOUSLY WHILE DRIVING ONE MEMBER OF THE GEAR SET AND BRAKING THE OTHER MEMBER. AN EXPENSIVE AND NON-HAZAROUS AQUEOUS SOLUTION IS USED TO REMOVE LAPPING COMPOSITION AFTER THE LAPPING OPERATION.

United States Patent US. Cl. 51-281 5 Claims ABSTRACT OF THE DISCLOSUREGear teeth of automotive hypoid gear sets are lapped with an aqueousbase lapping composition. The lapping composition is appliedcontinuously while driving one member of the gear set and braking theother member. An inexpensive and non-hazardous aqueous solution is usedto remove lapping composition after the lapping operation.

SUMMARY OF THE INVENTION This is a division of application S.N. 494,246,filed Oct. 8, 1965, now US. Pat. No. 3,462,251.

This invention concerns a process for lapping ferrous metals and alapping composition useful in that process. This process is particularlyuseful in lapping the gear teeth of hypoid gearsets extensively used inthe differentials of automobiles trucks and other vehicles.

Lapping ferrous metals and alloys susceptible to corrosion hastraditionally been done with lapping compositions prepared from oilbases thickened with grease or clay. Aqueous base lapping compositionscontaining glycols or alcohols have been used as lapping pastes fornonferrous but have not attained success as pumpable lappingcompositions for use on ferrous surfaces because of inferior lappingproperties and corrosion tendencies.

Lapping properties of lapping compositions are particularly criticalwhen lapping the gear teeth of hypoid gearsets used in rear axles ofautomotive vehicles. Unless properly lapped, these hypoid gearsetsproduce objectionable noise and have a significantly decreased usefullife. In the past, only specially formulated oil base lappingcompositions have been capable on a commercial basis of supplying thelapping properties essential to lapping hypoid gearsets.

This invention provides a process for lapping ferrous metals whichcomprises preparing a lapping composition consisting essentially of asuspension of water emulsifiablc oil and particulate abrasive in athickened aqueous base, applying said composition to a surface of saidferrous metal and moving said composition relative to said surface toeliminate surface roughness remaining after machining.

Use of the process of this invention decreases the cost of the overalllapping operation since removal of lapping composition from lappedmetals can be accomplished by washing with aqueous solutions. Dryingparts lapped by this process can be accomplished without causingabnormal health hazards or dangers since a major portion of the vaporsbeing removed is Water. When used to lap hypoid gearsets for thedifferentials of automobiles and other vehicles, this process producesgears having excellent noise properties. In a comparative test involvingover 80,000 gearsets, 92. 3% of the hypoid gearsets lapped by theprocess of this invention had satisfactory noise ratings as comparedwith 89.3% of gearsets lapped with an oil base lapping composition usinga similar process.

3,618,272 Patented Nov. 9, 1971 DETAILED DESCRIPTION Lappingcompositions used in the process of this invention are pumpable liquidsand are particularly useful in lapping operations where continuousapplication of lapping composition is required or beneficial. For thispurpose, these compositions preferably have a viscosity of about to 1000centipoises at 25 C. measured with a Brook-field viscometer using anumber 3 spindle rotating at 60 rpm. High heat capacity and coefficientof heat conductivity imparted to these compositions by the aqueous baseprovide lapping temperatures cooler than similar oil base compositions.

Most of the gear lapping machines designed to use oil base lappingcompounds can be adapted to use the process and composition of thisinvention by simply replacing the oil base compound with the aqueousbase compositions of this invention and making any adjustmentsnecessitated by a change in lapping composition viscosity, if any.Machine Models 17, 19' and 503 produced by Gleason Works, Rochester,N.Y., for lapping hypoid gearsets are readily adaptable to the use ofthe process of this invention in which composition is continuouslyapplied during the lapping operation.

Hypoid gears are ordinarily lapped at either 625 or 1250 pinion gearrevolutions per minute in these Gleason machines using the process ofthis invention. The gears are mounted in meshing relationship with eachother, and a load is applied to the gear teeth by driving the piniongear and braking the ring gear with a torque of about 40 to 90 inchpounds depending primarily on the size of the gearset. Lapping motion isimparted to the composition by relative movement of the meshing gearteeth. Each gearset is rotated for about 6 minutes under this loadresulting in removal of about 2.5 to 4 grams of metal from anaverage-size passenger car set.

Typical thickeners for the lapping compositions used in this inventioninclude polysaccharide gums such as xanthan gum, gum tragacanth and gumarabic; gelatin; starch; sodium or potassium salts of fatty acids suchas oleic acid; clays such as bentonite; salts of sulfonated polymers ofalkenyl aromatic compounds; and mixtures of these. The phrase thickenedaqueous base is used in this application to define aqueous basescomprising thickeners dissolved or mixed therein to increase theviscosity.

In these lapping compositions the most desirable thickener is xanthangum, a polysaccharide gum derived from Xanthomonas Campestris,commercially available under the trade name Kelzan from Kelco Company,Chicago. The term polysaccharide gum is used in this application todefine polysaccharides which have been partially oxidized and aretherefore soluble in Water. Lapping compositions comprising xanthan gumare particularly stable over a wide range of temperature, pH andmetal-ion concentration and are extremely desirable Where relativelycontinuous lapping of gearsets by the process of this invention is beingconducted. A small amount of thickener, usually less than one Weightpercent based on the total weight of the lapping composition, issufiicient to provide bases having adequate suspending ability althoughgreater proportions can be used.

Abrasives useful in this invention include materials such as siliconcarbide, boron carbide, diamond powder, aluminum oxide, silicon dioxide,ferric oxide, powdered glass, powdered mica, zirconium silicate, quartzand emery flour. Recovery of the more expensive abrasives from thewashing solutions by processes simplified because of the aqueous natureof the lapping composition renders the use of such abrasiveseconomically feasible in the process of this invention. Particle size ofabrasives in the process of this invention is preferably from about toless than 300 mesh for good stability. Silicon carbide abrasives havinga starting particle size of about 240 mesh are preferred for lappinghypoid gearsets for rear axles using the process of this inventionbecause of good stability and excellent rear axle noise characteristics.

Thickened aqueous bases for the lapping compositions of this inventioncan suspend over 50% by weight of particulate abrasive. Suspending 50%by weight of silicon carbide having a particle size of about 240 mesh inthese aqueous bases increases the viscosity by about 150 centipoises at25 C. measured with a Brookfield viscometer using a number 3 spindlerotating at 60 r.p.m. Storage or nonuse of these lapping compositionsfor several days sometimes allows the abrasive particles to settle. Whenthis occurs, resuspension is accomplished by an ordinary agitatin.

Typical emulsifiable oils useful in the compositions of this inventionare the sulfonated paraffin or petroleum oils. The phrase emulsifiableoil is used in this application to define oils capable of formingsuspensions of fine oil particles in water and includes what arecommonly known as soluble oils. These emulsifiable oils decrease thetendency of the lapping compositions used in this invention to corrodeferrous parts and to change viscosity by water evaporation. A minimum ofabout by weight of emulsifiable oil based on the weight of the aqueousphase is desirable when lapping hypoid gearsets.

If desired, small amounts of preservatives such as formaldehyde and rustpreventatves such as sodium mercaptobenzothiazole can be added to thecompositions used in this lapping process.

Lapping compositions of this invention are prepared by slowly mixing asuitable thickener with water; stirring in an emulsifiable oil and othercorrosion inhibitors and preservatives, if desired; adjusting theviscosity with water; and stirring in the abrasive. Heating the waterprovides more rapid dissolution of thickener.

The lapping compositions of this invention generally are non-Newtonianfluids. To specify the viscosity of non- Newtonian fluids it isnecessary to include the rate of shear at which the viscosity value ismeasured. Specifying the spindle number and its revolutions per minuteused in the Brookfield viscometer measuring the viscosity identifies therate of shear. Brookfield viscometers are manufactured by the BrookfieldEngineering Laboratories, Inc., Stoughton, Mass.

EXAMPLE About 80 gallons of hot water is added to a tank equipped with astirrer. Xanthan gum thickener (2.86 lbs.) is slowly added to this waterwith stirring over a tfive-minute period. Using a sifter, 11.45 lbs. ofbentonite clay is stirred into the solution. This addition is followedby separately stirring in 4.3 lbs. of sodium mercaptobenzothiazole, 3.4lbs. of formaldehyde and 74.7 lbs. of emulsifiable oil. The resultingbase is stirred for about two hours until all components are thoroughlyblended resulting in a viscosity of about 300 centipoises measured witha Brookfield viscometer at C. using a number 3 spindle rotating at 60r.p.m.

About 650 lbs. of silicon carbide abrasive having a particle size ofabout 240 mesh is suspended in this base by slowly adding the abrasivewith stirring over a twohour period. After the addition, stirring iscontinued for two more hours. Water is added to adjust the Brookfieldviscosity to about 400 centipoises.

Lapping sets of rear axle hypoid gears while mounted in meshingrelationship and by driving the pinion gear and braking the ring gear,using continuous application of this composition, produced gears havingexcellent noise properties. With periodic additions of water andcomposition, lapping was continued for over a month with no decrease inlapping efiiciency. Lapping composition is removed from lapped gearsetsby passing them through a water base alkaline cleaner bath followed by adrying operation.

What is claimed is:

1. A process for lapping hypoid gearsets having a pinion gear and a ringgear which comprises preparing a lapping composition consistingessentially of a suspension of water emulsifiable oil and particulateabrasive in a thickened aqueous base by mixing a thickener selected fromthe group consisting of a polysaccharide gum, gelatin, starch, alkalimetal salt of a fatty acid, clay, salt of alkenyl aromatic sulfonatedpolymers and mixtures thereof into water, adding an emulsifiable oilselected from the group consisting of sulfonated parafiin and petroleumoils to the mixture, producing an emulsion of the oil in the water, andadding particulate abrasive made from silicon carbide, boron carbide,diamond powder, aluminum oxide, silicon dioxide, ferric oxide, glass,mica, zirconium silicate, quartz, or emery flour, said suspension havinga viscosity of about to 1000 centipoises measured with a Brookfieldviscometer at 25 C. using a number 3 spindle rotating at 60 r.p.m.,continuously applying said suspension to the teeth of the gears in saidgearset, holding said gears in meshing relationship with each other, anddriving the pinion gear while braking the ring gear.

2. The process of claim 1 in which the thickened aqueous base isprepared by mixing an xanthan gum thickner with water.

3. The process of claim 2 in which the particulate abrasive is siliconcarbide particles having a particle size between about and 300 mesh.

4. The process of claim 3 in which the thickened aqueout base isprepared by adding the emulsifiable oil in an amount of at least 10weight percent of the water and thickener.

5. The process of claim 4 comprising removing the lapping compositionfrom lapped gearsets by passing the gearsets through an aqueous basecleaner bath.

References Cited UNITED STATES PATENTS 2,141,729 12/1938 Thompson 5 13022,443,698 6/ 1948 Snyder 5 l304 2,765,223 10/1956 Candee et al 5l3042,942,389 6/1960 Praeg et 'al. 5l287 2,984,956 5/1961 Schicht 5l2873,265,475 8/1966 Schantz 51-306 3,345,146 10/1967 Gardille 51-306 DONALDJ. ARNOLD, Primary Examiner US. Cl. X.R.

